Super microfilaments have been used in various applications such as artificial leathers, wiping cloths or filters. However, since special and complicate spinning methods such as islands-in-a-sea type fiber spinning (for example, Japanese Patent Laid-Open No. Hei 7-258940) or spinning by dividual fibers (for example, Japanese Patent Laid-Open No. 2002-220740) have been used, for the production of highly oriented super micro filaments and having high quality with the filament diameter of 5 μm or less, they are expensive and cannot be drawn simply and conveniently by using general-purpose fibers.
On the other hand, as a method of obtaining fibers of high tensile strength and high tensile modulus, the present inventors, et al. have proposed a zone drawing method (Japanese Patent Publication No. Sho 60-24852), but further requirements are desirable for stable production of fine filaments by the zone drawing. Further, while the present inventors have already disclosed a prior invention for the method of obtaining super micro filaments (Japanese Patent Application No. 2001-353781), it has been found that further requirements are desirable for obtaining stable super micro filaments continuously.